Perhaps the unbroken circle with a “U” is some remnant of a valiant attempt to align with US chart symbology: https://www.faa.gov/air_traffic/flig...g-complete.pdf
My brief research suggests that the interesting question is: Where did the broken circle symbology on Australian charts come from (apart from the obvious)? My wild guess is that CaptainMidnight, alphacentauri or Vag277 might have some insights.
